Role of external aeration in iron-electrocoagulation for treating synthetic dye wastewater

An external aeration-assisted electrocoagulation (EC) process using Fe-Fe electrodes was investigated for the efficient treatment of representative dyes, namely Congo Red (CR), Rhodamine B (RhB), and Direct Red 31 (DR 31). The role of external aeration was critically examined to understand its influence on degradation efficiency and reaction pathways. Optimal operating conditions were identified as near-neutral pH (7.4), an applied voltage of 1.5 V, an initial dye concentration of 25 mg L−1, and a reaction time of 60 minutes. Under these conditions, complete color removal of CR was achieved within 60 minutes, while RhB and DR 31 reached complete color removal within 45 minutes. Furthermore, complete COD removal for all dyes within 60 minutes confirmed effective mineralization rather than partial degradation. Reactive species scavenging experiments revealed that ferryl ions (Fe4+) were the dominant oxidative species responsible for dye breakdown, while anodic iron dissolution played a crucial role by generating in situ coagulant and oxidizing species. External aeration enhanced oxygen availability, mass transfer, and reactive intermediate formation, resulting in accelerated degradation kinetics. Overall, the study demonstrates that aeration-assisted Fe – Fe EC is an energy-efficient, low voltage, and environmentally sustainable approach for the complete removal of dye pollutants from wastewater.